This invention relates to detergent formulations employing a particular aminocarboxylic acid as a builder component.
The use of builders as additives to soap and synthetic surfactants, and the property which some materials have of improving detergency levels of such detergent formulations are well known phenomena. The phenomena are widely appreciated but the exact behavior and mechanics of how builders perform their function have never been fully explained. While many explanations for the behavior of builders may be found, there still has not been determined a set of criteria which would permit one to accurately predict which compounds actually possess builder properties.
In view of the many factors which contribute to improving the cleaning power of surfactants, and in view of the most recent art in this field, it is necessary for a builder to meet certain requirements, including the ability to:
(1) sequester the hardness-inducing agents of the water, such as calcium and magnesium ions; PA1 (2) disperse pigment dirt particles, which are the principal constituents of the dirt of fabrics, in the wash-bath; PA1 (3) stabilize the dirt removed in the wash-bath and prevent dirt particles from redepositing on the fiber; PA1 (4) inactivate mineral matter being contained in the wash-bath; and PA1 (5) reduce the precipitation of surfactants. PA1 (1) The polyethylene oxide condensates of alkylphenols, e.g., the condensation products of alkylphenols or dialkylphenols wherein the alkyl group contains from about 6 to 12 carbon atoms in either a straight chain or branched chain configuration, with ethylene oxide, the ethylene oxide being present in amounts equal to about 3 to 25 moles of ethylene oxide per mole of alkylphenol. PA1 (2) The condensation product of aliphatic alcohols having from 8 to 18 carbon atoms, in either straight chain or branched chain configuration, with ethylene oxide, e.g., a coconut alcohol-ethylene oxide condensate having from about 3 to 30 moles of ethylene oxide per mole of coconut alcohol, the coconut alcohol fraction having from 10 to 14 carbon atoms. PA1 (3) Long chain tertiary amine oxides corresponding to the following general formula, R.sub.1 R.sub.2 R.sub.3 N.fwdarw.O, * wherein R.sub.1 is an alkyl radical of from about 8 to 18 carbon atoms, and R.sub.2 and R.sub.3 are each methyl or ethyl radicals. Examples of amine oxides suitable for use in this invention include dimethyldodecylamine oxide, dimethyloctylamine oxide, dimethyldecylamine oxide, dimethyltetradecylamine oxide, dimethylhexadecylamine oxide. PA1 (4) Long chain tertiary phosphine oxides corresponding to the following general formula RR'R"P.fwdarw.O wherein R is an alkyl, alkenyl or monohydroxyalkyl radical ranging from 10 to 18 carbon atoms in chain length and R' and R" are each alkyl or monohydroxyalkyl groups containing from 1 to 3 carbon atoms. Specific examples can be found in U.S. Pat. No. 3,159,581. FNT *The arrow in the formula is a conventional representation of a semi-polar bond. PA1 (a) The surfactant solution consisted of 3.0 g of Tergitol*** 25-L-5 and 20 g of a 40% solution of sodium xylene sulfonate diluted with water to a final volume of 250 ml. Five ml of the surfactant solution was added to each washing vessel resulting in a working surfactant concentration of 60 mg surfactant per liter. PA1 (b) Builders were added to the surfactant solution just prior to swatch addition to the wash solution. All builders were solutions of between 5-40% active builder by weight which had been previously adjusted to pH of approximately 11.0 using NaOH. In order to better control pH throughout the wash cycle and minimize pH buffering differences between various builders, 25% or 250 ml of the wash solution was composed of a pH 10.0 buffer solution containing borax and NaOH (see Lange's Handbook of Chemistry, 12th ed., 1979, Section 5, page 78). Builder concentrations were varied for the different experiments. FNT *Cloth swatches were obtained from Testfabrics Inc., Middlesex, New Jersey. FNT **Terg-o-tometer, Model 7243, manufactured by United States Testing Company, Inc. FNT ***Trademark for a nonionic surfactant, an ethoxylated alcohol, manufactured by Union Carbide Corporation.
The two most commonly employed types of surfactants are anionic and nonionic. The former can be broadly described as the water-soluble salts, particularly the alkali metal salts of organic sulfuric reaction products having in their molecular structure an alkyl radical containing from about 8 to about 22 carbon atoms and a radical selected from the group consisting of sulfonic acid and sulfuric acid ester radicals. Included in the term alkyl is the alkyl portion of higher acyl radicals. Important examples of such surfactants are the sodium alkyl sulfates, especially those obtained by sulfating the higher alcohols (C.sub.3 -C.sub.13 carbon atoms) produced by reducing the glycerides of tallow or coconut oil; sodium or potassium alkylbenzenesulfonates, in which the alkyl group contains from about 9 to about 15 carbon atoms, sodium alkylglycerylethersulfonates, especially those ethers of the higher alcohols derived from tallow and coconut oil; sodium coconut oil fatty acid monoglyceride sulfates and sulfonates; sodium or potassium salts of sulfuric acid esters of the reaction product of one mole of a higher fatty alcohol (e.g., tallow or coconut oil alcohols) and about 1 to 6 moles of ethylene oxide; sodium or potassium salts of alkylphenol ethylene oxide ether sulfate with about 1 to about 10 units of ethylene oxide per molecule and in which the alkyl radicals contain about 9 to about 12 carbon atoms; the reaction product of fatty acids esterified with isethionic acid and neutralized with sodium hydroxide, where, for example, the fatty acids are derived from coconut oil; sodium or potassium salts of fatty acid amide of a methyltauride in which the fatty acids, for example, are derived from coconut oil.
Nonionic surfactants may be broadly defined as compounds aliphatic or alkyl aromatic in nature which do not ionize in water solution.
For example, a well known class of nonionic synthetic detergents is available on the market under the trade name of "Tergitol"*. These compounds are formed by condensing ethylene oxide, alternatively propylene oxide, with an alcohol. The hydrophobic portion of the molecule which exhibits water insolubility has a total carbon chain length of from about 8 to about 20 carbon atoms. The addition of polyoxyethylene radicals to the hydrophobic portion tends to increase the water solubility of the molecule as a whole. The method of making such surfactants is well known to the art, comprising reacting the alkylene oxide and the long chain alcohol together in the presence of an acid catalyst, e.g. BF.sub.3. FNT *Trademark of Union Carbide Corporation
Other suitable nonionic surfactants include:
Builders are formulated with such surfactants to enhance their cleaning capabilities. Among the builder materials described in the prior art, are water-soluble inorganic alkaline builder salts which are used alone or in combination. Examples are alkali metal carbonates, borates, phosphates, polyphosphates, bicarbonates and silicates.
Various organic compounds have already been suggested for use as builders, e.g. nitrilotriacetic acid (NTA), ethylenediaminetetracetic acid (EDTA), citric acid, oxydiacetic acid, oxydisuccinic acid, and polymeric carboxylic acids. Additional builders are indicated in U.S. Pat. No. 4,265,776.
As previously noted, NTA is recognized as an efficient detergent builder. Unfortunately, initial toxicity studies (performed when NTA was just beginning to be seriously considered as a detergent builder replacement for phosphates) linked NTA to cancer. This resulted in a voluntary ban on use of NTA in detergents by major detergent manufacturers. The search for an efficient non-phosphorus containing builder thus continues. Naturally other lower molecular weight aminopolycarboxylic acids were tested, such as EDTA and diethylenetriaminepentaacetic acid (DTPA).* However, their performance was less than satisfactory. As a result of these tests it has been generally assumed that as the molecular weight of the polyaminocarboxylic acid increased, the building efficency decreased. FNT *Methods of making these carboxylic acid derivatives of amines are found in Chelating Agents and Metal Chelates, Ed. Dwyer, F. P. and Mellor, D. P., Academic Press, New York, N.Y. (1964), pp. 285-288.
It has now been found that, unexpectedly, triethylenetetraminehexaacetic acid (TTHA) is superior to both the EDTA, DTPA and the next higher member of the series, which is tetraethylenepentamineheptaacetic acid (TPHA).